For two years, a zoo in southern Japan had been puzzled by a mystery: How did Momo, a gibbon kept alone in her cage, get pregnant?. The 12-year-old white-handed gibbon lived by herself and was never joined by a companion. Some of her neighbors are males, sure, but their cages are separated by sturdy bars and jagged chicken wire fencing. It was inconceivable to the zookeepers that they could have mated through the two layers of barriers. She gave birth in 2021 to a yet unnamed male gibbon with black hair and white fur trimming around its face.